Showing papers by "University of North Carolina at Greensboro published in 1999"
TL;DR: This paper examined the antecedents, consequences, and mediational role of team empowerment using 111 work teams in four organizations and found that empowered teams were more productive and proactive than less empowered teams and had higher levels of customer service, job satisfaction and organizational and team commitment.
Abstract: We examined the antecedents, consequences, and mediational role of team empowerment using 111 work teams in four organizations. The results indicated that the actions of external leaders, the production/service responsibilities given to teams, team-based human resources policies, and the social structure of teams all worked to enhance employee team empowerment experiences. More empowered teams were also more productive and proactive than less empowered teams and had higher levels of customer service, job satisfaction, and organizational and team commitment.
1,793 citations
TL;DR: The usefulness of the in vitro digestion process as a rapid and cost-effective model for screening the bioavailability of carotenoids from meals is supported.
Abstract: The objective of this study was to develop a model for assessing the bioavailability of carotenoids from meals using an in vitro digestion procedure. A meal was prepared using baby food carrots, spinach, and a meat, plus tomato paste. The aqueous fraction was isolated from digesta to determine the quantity of carotenoids transferred from the food to micelles. The micellarization of lutein (25-40%) exceeded (p < 0.01) that of alpha- and beta-carotene (12-18%) and lycopene (<0.5%). Micellarization of carotenoids was not affected by elimination of the gastric phase of the digestive process. The absence of bile extract prevented the transfer of carotenoids from foods to micelles, whereas omission of pancreatin only reduced the micellarization of the carotenes. Differentiated cultures of Caco-2 human intestinal cells accumulated 28-46% of micellarized carotenoids from the medium after 6 h. These results support the usefulness of the in vitro digestion process as a rapid and cost-effective model for screening the bioavailability of carotenoids from meals.
476 citations
TL;DR: This article examined if mental skills and strategies such as high confidence, commitment, and the use of cooperative routines, as well as previously unexamined physical, social, and environmental factors affect Olympic performance.
Abstract: This study was designed to examine if mental skills and strategies such as high confidence, commitment, and the use of cooperative routines, as well as previously unexamined physical, social, and environmental factors affect Olympic performance. Athletes and coaches from 8 Atlanta US Olympic teams were interviewed. Four teams met/exceeded performance expectations and 4 teams failed to perform up to performance predictions. Focus group interviews were conducted with 2 to 4 athletes from each team. Individual interviews were conducted with 1 or 2 coaches from each team. Each interview was recorded, transcribed, and analyzed by three trained investigators using hierarchical content analyses. Differences existed between teams that met/exceeded performance expectations and teams that failed. Teams that met/exceeded expectations participated in resident training programs, experienced crowd and family or friend support, utilized mental preparation, and were highly focused and committed. Teams that failed to meet...
400 citations
TL;DR: In this paper, the authors investigated the impact of a first child's birth on the marriage and found that the change in the marital relationship was related to whether the pregnancy was planned, to depressive symptoms of spouses, to the couple's problem-solving behavior, and to the gender of the child.
Abstract: Observed interaction of couples during a problemsolving task and self-reports of spouses concerning their marriage were investigated before the birth of their first child and at 3, 12, and 24 months after the birth of the child. The study focuses on the impact of a first child's birth on the marriage. Hierarchical linear model analyses were performed. Patterns of change in the marital relationship were related to whether the pregnancy was planned, to depressive symptoms of spouses, to the couple's problem-solving behavior, and to the gender of the child. There is a long history of research on the transition to parenthood as a crisis for couples, and the premise of much of that literature is that becoming a parent is a risk factor for individual and marital distress. Many cross-sectional studies have documented the negative correlation between the presence of children and marital satisfaction (e.g., Glenn & McLanahan, 1982; Miller, 1976). Additionally, several longitudinal studies that followed couples from before the birth of the child through a period after the birth show overall linear declines in marital satisfaction (Belsky, Lange & Rovine, 1985; Cowan et al., 1985; Feldman & Nash, 1984). More recently, however, scholars are calling for studies that go beyond documenting declines in marital satisfaction and that illuminate the variety of adaptations couples make and the factors related to different adaptations (Belsky & Rovine, 1990; Cox, 1985; Huston & Vangelista, 1995; Cowan & Cowan, 1992). Not only each partner's satisfaction with the marriage should be of interest, but also observations of the couple's interactions. In the study presented here, both spouses' perceptions of their marriage and their behavior during a marital problem-solving task were investigated before the birth of their first child and at 3, 12, and 24 months after the birth. The study focused on the impact of a first child's birth on the marnage. We assumed that couples would show a variety of adaptations. BACKGROUND Patterns of Change Transitions are times when a marriage may be particularly vulnerable because the relationship has to be reorganized to meet new challenges. Yet, parenthood actually may enhance some relationships, undermine others, and have little effect on others (Cox, 1985; Huston & Vangelisti, 1995). Some couples may develop new skills in resolving problems, for example, and others may find resolving problems a major difficulty. As Cowan (1991) has noted, "a central task for researchers is to determine the conditions under which both normative and nonnormative events stimulate developmental advances, produce dysfunctional crises, or leave the individual and the family relatively unchanged" (p. 5). Identifying couples who are likely to experience increased marital difficulty in the transition to parenthood is important in order to focus preventive efforts on the most vulnerable couples. At the same time, understanding the strengths of couples whose relationships are enhanced by the experience of parenthood or for whom the experience has minimal negative impact also may inform intervention. Couples who not only show distress in response to the birth of a child, but who also fail to show recovery over time may be of particular concern. Initial difficulties in a transition may be normative, but the lack of reorganization over time may be a sign of chronic problems that are likely to influence parenting and child development negatively. The possibility of such different patterns highlights the importance of considering transitions as processes over time (Cox, 1985) and the importance of using methods that can capture this process. When data are gathered from parents on only one or two occasions soon after the birth of the child, short-term fluctuations in satisfaction may be detected, but more gradually emerging effects remain undiscovered. If one expects an initial change in the marital relationship followed by recovery over the first 2 years, data that longitudinally cover that period are needed. …
341 citations
TL;DR: The games for understanding group scored significantly higher on passing decision making than the technique and control groups during posttest game play and significantly higher than the control group for declarative and procedural knowledge.
Abstract: The purpose of this study was to test the validity of the games for understanding model by comparing it to a technique approach to instruction and a control group. The technique method focused primarily on skill instruction where the skill taught initially was incorporated into a game at the end of each lesson. The games for understanding approach emphasized developing tactical awareness and decision making in small game situations. Two physical education specialists taught field hockey using these approaches for 15 lessons (45 min each). The control group did not receive any field hockey instruction. Data were collected from 71 middle school children. Pretests and posttests were administered for hockey knowledge, skill, and game performance. Separate analyses of variance or analyses of covariance were conducted to examine group differences for cognitive and skill outcomes. The games for understanding group scored significantly higher on passing decision making than the technique and control grou...
261 citations
TL;DR: Overexpression of p53 causes G2 arrest, attributable in part to the loss of CDC2 activity, and targeting cyclin B1 to the nucleus in cells also expressing CDC2 T14A Y15F did overcome this arrest.
Abstract: Overexpression of p53 causes G2 arrest, attributable in part to the loss of CDC2 activity. Transcription of cdc2 and cyclin B1, determined using reporter constructs driven by the two promoters, was suppressed in response to the induction of p53. Suppression requires the regions -287 to -123 of the cyclin B1 promoter and -104 to -74 of the cdc2 promoter. p53 did not affect the inhibitory phosphorylations of CDC2 at threonine 14 or tyrosine 15 or the activity of the cyclin-dependent kinase that activates CDC2 by phosphorylating it at threonine 161. Overexpression of p53 may also interfere with the accumulation of CDC2/cyclin B1 in the nucleus, required for cells to enter mitosis. Constitutive expression of cyclin B1, alone or in combination with the constitutively active CDC2 protein T14A Y15F, did not reverse p53-dependent G2 arrest. However, targeting cyclin B1 to the nucleus in cells also expressing CDC2 T14A Y15F did overcome this arrest. It is likely that several distinct pathways contribute to p53-dependent G2 arrest.
186 citations
TL;DR: A novel posttranslational mechanism of copper homeostasis in vivo consistent with the proposed function of the Wilson's disease protein in holoceruloplasmin biosynthesis and biliary copper excretion is revealed and is of relevance to the broad clinical heterogeneity observed in this disease.
Abstract: Wilson’s disease is an inherited disorder of copper metabolism characterized by hepatic cirrhosis and neuronal degeneration. In this current study, a polyclonal antiserum specific for the Wilson’s ...
178 citations
TL;DR: In this article, an experiential approach, which grounds measurement in women's lived experiences, improves our ability to conduct research that correctly identifies, monitors, and explains the epidemiology of this phenomenon and provides a solid basis for policy and program development.
Abstract: Many areas of women's health, including battering, suffer from conceptual and methodological deficits. This article uses the "measurement trap" (Graham & Campbell, 1991), a set of conditions defined by lack of information resulting from a narrow conceptualization of the problem, poor existing data sources, inappropriate outcome indicators, and limited measurement techniques, as a framework for describing how current approaches to conceptualizing and measuring battering hamper research and program efforts in the field of domestic violence. We then describe an alternative conceptualization-and-measurement approach that is based on battered women's experiences. We argue that an experiential approach, which grounds measurement in women's lived experiences, improves our ability to conduct research that correctly identifies, monitors, and explains the epidemiology of this phenomenon and provides a solid basis for policy and program development.
174 citations
TL;DR: In this article, the authors report the findings of a study regarding the reactions of 492 line-level employees from two Fortune 500 organizations in response to the organizations' recent implementation of self-managing work teams (SMWTs).
Abstract: This paper reports the findings of a study regarding the reactions of 492 line‐level employees from two Fortune 500 organizations in response to the organizations’ recent implementation of self‐managing work teams (SMWTs). As predicted, we found that anticipatory injustice was significantly positively related to change‐resistance and turnover intentions; and significantly negatively related to employees’ commitment; and that procedural justice can mitigate the latter relationships. Implications for managing change are discussed.
163 citations
TL;DR: The traditional dietary antioxidants most commonly investigated to inhibit free-radical damage are vitamin E, vitamin C, and beta carotene and other nutritional agents have also been noted to contain antioxidant properties.
Abstract: Several mechanisms have been forwarded to explain the etiology of exercise-induced muscle damage. Free-radical mediated processes appear to be an important component of the inflammatory mediated re...
152 citations
TL;DR: The findings support the hypothesis that executive function deficits may precede the onset of schizophrenia and related illnesses.
TL;DR: Women's present levels of distress and coping strategies should be assessed prior to initiating infertility treatment to provide the patients with opportunities to learn and practice new adaptive behaviors that could enhance their ability to cope with infertility and the associated medical procedures.
TL;DR: It is argued and shown that different properties of stimuli are compatible with different types of processing, and that single-process models should be extended to take this interplay into account.
TL;DR: In this article, the authors examined whether individuals' marital functioning related to both their own and their partner's attachment stance in a sample of 138 couples and found that wives of continuous-secure husbands exhibited more positive marital behavior than wives of dismissing and earned secure husbands.
Abstract: In a sample of 138 couples, the present study examined whether individuals' marital functioning related to both their own and their partner's attachment stance. Earned-secure wives managed their affect as well as continuous-secure wives during problem-solving discussions and better than preoccupied or dismissing wives. However, preoccupied and dismissing wives did not exhibit markedly different patterns of affect regulation in their marriages. Regarding individuals' marital functioning and partners' attachment stance, neither husbands' behavior nor perceptions related to their wives' attachment stance. However, wives of continuous-secure husbands exhibited more positive marital behavior than wives of dismissing and earned-secure husbands. Findings are discussed in terms of how attachment working models may account for both continuities and discontinuities between earlier caregiving experiences and functioning in adult relationships.
TL;DR: It is shown that GFP fluorescence can indicate expression of the Bacillus thuringiensus cry1Ac gene when co-introduced into tobacco and oilseed rape, as demonstrated by insect bioassays and western blot analysis.
Abstract: The use of transgenic crops has generated concerns about transgene movement to unintended hosts and the associated ecological consequences. Moreover, the in-field monitoring of transgene expression is of practical concern (e.g., the underexpression of an herbicide tolerance gene in crop plants that are due to be sprayed with herbicide). A solution to these potential problems is to monitor the presence and expression of an agronomically important gene by linking it to a marker gene, such as GFP. Here we show that GFP fluorescence can indicate expression of the Bacillus thuringiensus cry1Ac gene when co-introduced into tobacco and oilseed rape, as demonstrated by insect bioassays and western blot analysis. Furthermore we conducted two seasons of field experiments to characterize the performance of three different GFP genes in transgenic tobacco. The best gene tested was mGFP5er, a mutagenized GFP gene that is targeted to the endoplasmic reticulum. We also demonstrated that host plants synthesizing GFP in the field suffered no fitness costs.
TL;DR: In this paper, the authors studied the impact of global warming on lakes and streams in the foothills near Tookik Lake, Alaska, at 68°N and found that removing lake trout results in a striking increase in abundance and productivity of smaller fish, including small lake trout, and the emergence of burbot as an alternate top predator.
Abstract: Lakes and streams in the foothills near Tookik Lake, Alaska, at 68°N have been studied since 1975 to predict physical, chemical and biological impacts of future global change. Experimental manipulations include whole lake and continuous stream fertilization as well as removal and addition of predators (copepods, lake trout, grayling, sculpin). Based on our evidence the following scenario is likely. Warming thaws the upper layers of permafrost and streams and lakes become enriched with phosphorus. Streams respond quickly with higher production of diatoms but animal grazers keep biomass changes to a minimum. Fish productivity also increases. If phosphorus levels are too high, mosses become the dominant primary producer and sequester all of the nutrients. Growth of Arctic grayling under the present conditions only occurs in summers with higher than average stream flow. The present population would be stressed by warmer temperatures. When higher phosphorus levels reach lakes and cause slight europhication, the number of trophic levels will increase, especially within the microbial food web. Warmer lake temperatures increase stratification and, combined with eutrophication, could decrease oxygen in the hypolimnion. Oxygen levels will also decrease in winter under the ice cover. Eventually this habitat change will eliminate the lake trout, a top predator. Removal of lake trout results in a striking increase in abundance and productivity of smaller fish, including small lake trout, and the emergence of burbot as an alternate top predator. Large species of zooplankton will become virtually extinct.
TL;DR: It is determined that NO donors block pharmacologically induced metamorphosis in the mud snail Ilyanassa obsoleta, whereas injections of inhibitors of nitric oxide synthase (NOS) allow competent larvae to become juveniles.
Abstract: Metamorphosis is a crucial life-history event that can change an organism's form, function, behavior, and ecological interactions. In the Mollusca, several neurotransmitters and neuromodulators play inductive or inhibitory roles in the pathways that govern larval metamorphosis. Nitric oxide (NO) has been implicated in developmental processes in vertebrates and arthropods, but not previously in molluscs. We determined that NO donors block pharmacologically induced metamorphosis in the mud snail Ilyanassa obsoleta, whereas injections of inhibitors of nitric oxide synthase (NOS) allow competent larvae to become juveniles. We describe a new developmental role for NO, as an endogenous inhibitor of molluscan metamorphosis.
TL;DR: It is demonstrated that calcitriol-mediated A-to-B calcium transport in Caco-2 cells is a specific, transcellular process that requires transcriptional events normally mediated through the vitamin D receptor.
Abstract: Calcium transport in the apical-to-basolateral (A-to-B) or B-to-A direction was examined in cells treated with 10 nM 1,25-dihydroxyvitamin D3[1,25(OH)2D3, calcitriol] for up to 72 h. Net A-to-B cal...
TL;DR: In this article, the authors evaluated the effectiveness of a state independent living program (ILP) by comparing outcomes for program participants and nonparticipants in four core areas: housing, education, employment, and financial self-sufficiency.
TL;DR: In this article, the authors extended the Riggs and O'Leary model to premilitary experiences of IP violence among U.S. Navy recruits and found that verbal aggression was the single best predictor of aggression and physical aggression was second best predictor.
Abstract: Research on intimate partner (IP) aggression was extended to premilitary experiences of IP violence among U.S. Navy recruits. Riggs and O'Leary's (1989) model of courtship aggression was examined separately for men (N = 1,307) and women (N = 1,477). A test was conducted of the model using participant gender along with the significant variables from the initial analyses and the interaction of gender with each of these variables. Situational components explained more variance that did the background components. For women and men, the amount of variance accounted for was almost tripled after the addition of the situational factors. Partner aggression contributed to a substantial increase in the amount of variance. Partner's verbal aggression was the single best predictor of aggression, and partner's physical aggression was the second-best predictor. The situational component substantially increased the predictive power of the model. The results support the validity of the Riggs and O'Leary model.
TL;DR: The decision to accept treatment "at any cost" was incomparable with any other life decisions the couples had faced, and information regarding potential for cure and risk of recurrence were highly important factors in the decision process.
Abstract: Prostate cancer is a pressing health concern in the United States and one surrounded by continual Controversy. Currently there is no consensus regarding the efficacy of routine screening, nor has one treatment modality been demonstrated as superior. Patients and spouses are asked to choose from several options: radical prostatectomy, radiation therapy, or the “watch and wait” approach. A grounded theory design was used to examine the actual treatment decision-making process as it occurred over time among 18 newly diagnosed prostate cancer patients and their wives in western North Carolina. Couples were interviewed conjointly and individually to explore their perceptions of the decision process. All interviews were audiotaped, transcribed verbatim, and analyzed using content analysis techniques. Couples negotiated decisions through their common and unique personal and family histories, biases, and individual coping styles. They narrowed the options based on these factors. Most couples received their counse...
TL;DR: This paper found that the state unemployment rate has a clear effect on retrospective evaluations of national economic conditions and that the contextual patterning of information, perhaps especially through media reporting of economic conditions, is responsible for producing this effect.
Abstract: The theoretical premise of this study is that individual retrospective evaluations of the national economy, which have a clear impact on voting behavior in national elections, are influenced not only by the national economy but also by the state and local economic context. This hypothesis is tested by analyzing the effect that the unemployment rate in the individual's state and community has on the individual's retrospective evaluation of the national unemployment situation in 1992, using data from the 1992 American National Election Study survey, supplemented with data on the unemployment rate during the third quarter of 1992 for the respondent's community and state. The findings show that the state unemployment rate has a clear effect on retrospective evaluations of national economic conditions. This effect occurs apart from any effect on fear of unemployment, which is unaffected by the state unemployment rate. The community unemployment rate has little or no effect on retrospective economic evaluations, except for a small impact on personal unemployment experience. The contextual effect that we observe therefore is primarily sociotropic, not personal pocketbook, in nature. We suggest that the contextual patterning of information, perhaps especially through media reporting of economic conditions, is responsible for producing this effect.
TL;DR: An alternative view is presented here in which the stuctural relations among elements are an important factor in explaining the relative speeds of global and local processing, and subjects created equivalence classes of similar and proximate local elements before identifying the constituent elements.
TL;DR: This is a report of the process and evaluation of 12 years of mentoring new faculty in a university nursing faculty of 48 members, which finds that both new faculty and mentors at the end of the year are positive.
Abstract: This is a report of the process and evaluation of 12 years of mentoring new faculty in a university nursing faculty of 48 members. Each new faculty member is paired with an experienced faculty member who serves as a mentor for a year. Evaluations completed by both new faculty and mentors at the end of the year are positive.
TL;DR: The use of the Caco-2 human cell line as a model for studying the intestinal uptake, absorption, and possible interactions of dietary carotenoids is supported.
Abstract: Despite the interest in the diverse roles of dietary carotenoids in human health, little is known about the transfer of these plant pigments from foods to micelles during digestion and their subsequent transfer across the intestinal epithelium. We conducted this study to characterize the intestinal uptake of micellarized carotenoids using monolayers of differentiated Caco-2 human intestinal cells. Crystalline β-carotene (BC) and lutein (LUT), solubilized in mixed micelles for delivery to cells, were stable in a tissue culture environment for 20 hours. Cellular accumulation of micellar BC and LUT was proportional to the media content of carotenoids at ≤2 μmol/L and the length of exposure. Cellular accumulation of BC routinely exceeded LUT and was due in part to the enhanced efflux or possible metabolism of LUT. Cellular BC content increased in a curvilinear manner when cultures were incubated in micellar medium containing 2 to 27 μmol/L BC prepared from water miscible beadlets; cellular BC content was maximum when medium BC was ≥18 μmol/L. There was no indication that high levels of BC in medium or within cells adversely affected micellar LUT accumulation. These data support the use of the Caco-2 human cell line as a model for studying the intestinal uptake, absorption, and possible interactions of dietary carotenoids.
TL;DR: An improvement to the optimization problem of packing unequal spheres into a three-dimensional (3D) bounded region in connection with radiosurgical treatment planning is proposed that can greatly reduce its computation cost.
Abstract: We study an optimization problem of packing unequal spheres into a three-dimensional (3D) bounded region in connection with radiosurgical treatment planning. Given an input (R, V, S, L), where R is a 3D bounded region, V a positive integer, S a multiset of spheres, and L a location constraint on spheres, we want to find a packing of R using the minimum number of spheres in S such that the covered volume is at least V; the location constraint L is satisfied; and the number of points on the boundary of R that are touched by spheres is maximized. Such a packing arrangement corresponds to an optimal radiosurgical treatment planning. Finding an optimal solution to the problem, however, is computationally intractable. In particular, we show that this optimization problem and several related problems are NP-hard. Hence, some form of approximations is needed. One approach is to consider a simplified problem under the assumption that spheres of arbitrary (integral) diameters are available with unlimited supply, and there are no location constraints. This approach has met with certain success in medical applications using a dynamic programming algorithm (Bourland and Wu, 1996; Wu, 1996). We propose in this paper an improvement to the algorithm that can greatly reduce its computation cost.
TL;DR: A robust and efficient algorithm for calculating the centerline of a computer-generated colon model created from helical CT image data, which is an essential aid for navigating through complex anatomy such as the colon.
Abstract: We present a robust and efficient algorithm for calculating the centerline of a computer-generated colon model created from helical CT image data. The centerline is an essential aid for navigating through complex anatomy such as the colon. Our algorithm involves three steps. In the first step, we generate a 3D skeleton of the binary colon volume using a fast topological thinning algorithm. In the second step, we employ a graph search algorithm to remove extra loops and branches. These loops and branches are caused by holes in the object that are artifacts produced during image segmentation. In the final step, we compute a smooth representation of the centerline by approximating the skeleton with cubic B-splines. This final step is necessary because the skeleton contains many abrupt changes in direction due to the discrete nature of image data. The user supplies two endpoints for the centerline; otherwise, the algorithm is fully automated. Experimental results demonstrate that the algorithm is not only robust but also efficient.
TL;DR: It is suggested that 30 min of moderate-intensity exercise in female subjects can result in mild oxidative stress as indicated by blood glutathione status and that menstrual cycle phase has minimal influences on these exercise responses.
Abstract: Effect of exercise during the follicular and luteal phases on indices of oxidative stress in healthy women. Med. Sci. Sports Exerc., Vol. 31, No. 3, pp. 409-413, 1999.Purpose:Eleven healthy nonsmoking women (24 ± 1.1 yr) exercised for 30 min at 75-80% O2max during the follicular (F) and lute
TL;DR: Results from whole‐cell recording experiments suggested that OE2 caused the LTP‐suppressant effect through an action on NMDA‐mediated currents, and suggest an age‐dependent and possibly a surface membrane receptor‐mediated role for oestrogens in modulating the efficacy of input‐output properties of CA1 neurones produced by HFS during a critical period in development.
Abstract: Long-term potentiation (LTP) of hippocampal population spike responses and excitatory postsynaptic potentials (EPSPs) from area CA1 stratum pyramidale was induced in slices of rat hippocampus maintained in vitro following brief high-frequency stimulation (HFS) of the Schaffer collateral-commissural pathway. When administered to slices prior to HFS, 17β-oestradiol (OE2), at a concentration as low as 0.1 nm, suppressed the magnitude of the resultant HFS-induced potentiation in slices from prepubertal animals (3 and 4 weeks old) of both sexes.
OE2 did not suppress the induction of LTP in slices taken from the hippocampus of adult animals of either sex.
There was no similar suppressant effect of 17α-oestradiol (OE1), progesterone (PRG) or testosterone (TST) on LTP in the young animals, even at a concentration 100 times greater than was effective for OE2.
The anti-oestrogen compound tamoxifen (TMX; 1.0 and 10.0 μm), which acts principally at intracellular binding sites within the nucleus, was without effect in diminishing the suppressant effect of OE2 on LTP in slices from young animals.
The LTP observed in slices from both 3-week-old and adult rats was AP5 sensitive and thus was shown to be dependent on activation of NMDA receptors. Results from whole-cell recording experiments suggested that OE2 caused the LTP-suppressant effect through an action on NMDA-mediated currents.
These data suggest an age-dependent and possibly a surface membrane receptor-mediated role for oestrogens in modulating the efficacy of input-output properties of CA1 neurones produced by HFS during a critical period in development.
One class of compounds that has long been known to have endocrine functions related to mammalian reproductive systems is the steroid hormones. Amongst this family of molecules, there is additional evidence that oestrogens are present within the central nervous system and can produce rapid effects on neuronal excitability (Kelly et al. 1980; Smith et al. 1987; Wong & Moss, 1994). The oestrogens are distributed heterogeneously and have been proposed to play a role as synaptic transmitters or neuromodulators (McEwen, 1991; Wong & Moss, 1992; Fahey et al. 1995).
Oestrogen exerts diverse modulatory effects on developmental processes, e.g. pubertal onset and neuroendocrine release (Ramirez & Sawyer, 1965; Smith & Davidson, 1968; Docke et al. 1978; Kawakami et al. 1978). It has also been demonstrated to affect neuronal excitability (Kelly et al. 1977, 1980; Wong & Moss, 1992, 1994) and to influence certain aspects of learning and memory (Ball, 1926; van Haaren et al. 1988). For example, there is behavioural evidence that supports an involvement of oestrogens in suppressing (Zuckerman, 1952) or enhancing (Sherwin, 1988) performance on learning- and memory-related tasks. Silverman & Eals (1992) found that women who were in the menstruating phase of their cycles when oestrogen levels are low performed much better on a task involving mental rotation of a complex object than they did at other times, when oestrogen levels were higher. These and related functional observations in humans (Vazquez-Pereyra et al. 1995), plus other features of oestrogenic and related sex steroidal function in the neural and endocrine systems of developing (Morley et al. 1992) and mature (Isaacson et al. 1995) mammals, suggest that this steroid family has important roles in the modulation of brain mechanisms, particularly during ontogeny.
Whereas the induction of certain forms of long-term potentiation (LTP) in area CA1 of the rat hippocampus is known to involve NMDA receptors (Collingridge & Bliss, 1987), there have yet to be reported any studies on the possible pharmacological influence of gonadal steroids in modulating the input-output functions mediated in the hippocampus by the NMDA receptor during induction of synaptic plasticity (Smith, 1991). Even so, it is known that hippocampal dendritic spine density is regulated by OE2 via an NMDA receptor-dependent mechanism (Wooley & McEwen, 1994) and intracellular Ca2+ is increased during synaptic transmission by a modulatory action at the NMDA receptor in the presence of pregnenolone sulphate (Fahey et al. 1995). Such knowledge of a key role for oestrogenic substances in hippocampal plasticity would be valuable and potentially significant, given the wide variety of neuronal mechanisms that are affected by sex steroids in the normal development of the mammalian CNS (Ramirez & Sawyer, 1965; Smith & Davidson 1968; Greenstein et al. 1977; Morley et al. 1992), and in light of the inconsistencies in the data with oestrogen from behavioural studies, as referred to above. The present experiments were designed to examine possible alterations in the efficacy of synaptic transmission produced by oestrogen and related steroids in the hippocampus of developing and mature rats.